The heart has four valves--two on the right (the pulmonary and tricuspid) and two on the left (the aortic and mitral)--that control the flow of blood through the chambers of the heart and out to the body. Although any of these valves may fail to function properly, disease most commonly affects the valves on the left side of the heart. The valves may narrow (called stenosis); the valves may not close all the way (causing a backflow of blood called regurgitation); or the valves may close incorrectly (called prolapse). A heart murmur represents the sound that a leaky or narrowed heart valve makes as blood moves through it.
The Aortic and Mitral Valves
Aortic stenosis is a narrowing of the aortic valve, through which blood flows from the left ventricle of the heart to the aorta, the major artery whose branches supply blood to various parts of the body. Sometimes this narrowness is a congenital (i.e., inborn) defect, but more often the valve narrows as a consequence of aging, or of infections, such as rheumatic fever. Aortic stenosis results in the left ventricle having to work harder and harder to push blood out. As this occurs, the muscular walls of the ventricle thicken, increasing their requirement for oxygen. Symptoms of aortic stenosis include chest pain when the oxygen needs exceed the supply from the coronary arteries; fainting (syncope), if the valve becomes very narrow; and congestive heart failure, which usually does not occur unless the valve has been narrowed for many years. Valve replacement, either with a mechanical valve made of metal or plastic or with a valve from a pig, may provide substantial relief from such valvular conditions.
In mitral stenosis, the valve opening between the upper and lower chambers on the left side of the heart has become narrowed. The cause is generally rheumatic fever, which is now rare in most developed countries but is common in many parts of the world, or results from other degenerative diseases and aging. When mitral stenosis occurs, the narrow valve impedes the entry of blood into the left ventricle from the atrium. Pressure builds up behind the valve, leading to an elevation of pressure in the lungs. This in turn may lead to shortness of breath (dyspnea), which is one of the major symptoms of mitral stenosis. Often, however, it occurs without any symptoms.
In aortic regurgitation, the aortic valve fails to close completely after the heart has pumped blood out into the aorta. Blood leaks back from the aorta into the left ventricle. In mitral regurgitation, improper closure causes blood to leak from the left ventricle back into the left atrium. In either case, the valve does not close properly because of a physical change in its shape or its support. This change may be the result of rheumatic fever; an infection (endocarditis), which may leave the valve scarred; or a heart attack, which causes loss of supporting muscle tissue. In the mitral valve, the change may be the result of a heart attack, which causes a loss of muscle tissue, or a spontaneous rupture of one of the muscular chords (chordea tendineae) that normally act as guide wires to keep the mitral valve in place.
Major symptoms of defective mitral valves include fatigue, shortness of breath, and edema. Medications such as digitalis, diuretics, and angiotensin-converting enzyme (ACE) inhibitors can help alleviate symptoms. Some defective mitral valves can be reconstructed or, failing that, replaced by an artificial valve.
The Pulmonary and Tricuspid Valves
In the pulmonary and tricuspid valves, any narrowing is rare and almost always congenital. Leakage, or regurgitation, is unusual, but may occur when use of illicit intravenous drugs leads to infection that damages the valve. The infection, hallmarked by fever, often settles on these two valves because they are the first ones bacteria come in contact with as they travel through the bloodstream. If the valve becomes leaky, swelling of the abdomen and legs may occur. As with other valves, treatment can include replacement, but this is rare and usually not as effective as it is when the aortic or mitral valve is involved.
Treatment
There are several treatments currently used to improve the performance of defective or diseased valves. Drugs such as digitalis medications, vasodilators, diuretics, anticoagulants, and antiarrhythmics may be administered for valve disorders. Rather than being curative, however, the major functions of these drugs are to reduce the severity of the symptoms, possibly reduce the workload of the heart, and prevent complications.
Balloon valvuloplasty may be used to correct narrowing of the mitral valve and occasionally the aortic valve by partially clearing obstructions. In use, a deflated balloon attached to the end of a catheter is introduced through an artery into the heart to the center of the valve opening and then inflated. The inflated balloon presses back the calcium in the valve or corrects the anatomical deformity that has caused the narrowing.
Alternatively, the diseased valve may be replaced with an artificial valve. Valve-replacement surgery is usually recommended when the damage to the valve is sever enough to be potentially life-threatening, as in the case of severe aortic stenosis. The mitral and aortic valves are the heart valves that most often need to be replaced. Artificial valves have been in use since 1952, when Charles Hufnagel successfully replaced a patient's aortic valve with a caged-ball valve.
Another method for treating defective valves is through reconstruction, which is typically used on minimally calcified valves. One type of reconstructive surgery is known as annuloplasty. An annuloplasty is performed to correct mitral valve insufficiency and/or stenosis. Annuloplasty involves implanting an annuloplasty ring on the valve annulus. The annuloplasty ring is designed to support the functional changes that occur during the cardiac cycle: maintaining coaptation and valve integrity in systole while permitting good hemodynamics in diastole.
To perform a successful annuloplasty, the size of the valve annulus where the annuloplasty ring is to be implanted must be accurately measured. Sizing is achieved by measuring the width and the height of the anterior leaflet with sizing obturators or, in the vernacular, valve sizers. Once the size has been determined, a proper annuloplasty ring may be selected and implanted.
A conventional annulus sizer currently used in annuloplasty surgery is illustrated in FIGS. 1 and 2 and is generally referenced with numeral 10. The sizer 10 has a thickness T which is on the order of 0.28 inch and is made of a transparent polymer. The sizer 10 snaps onto a handle 12 with male and female couplers 14 and 16, respectively. The female coupler 16 is formed substantially in the centroid of the somewhat oval-shaped cross-section sizer 10, as shown in FIG. 2. In use, the surgeon estimates the valve annulus size and selects a sizer accordingly. The sizer is snapped onto the end of the handle and guided into proximity of the annulus, which may involve passing the sizer through a relatively small access channel, especially in minimally invasive surgical procedures. The final seating of the sizer in the annulus may necessitate viewing the annulus through the transparent sizer, though the polymer material is not a perfect transmitter of light. The sizer thickness serves to provide tactile feedback to the surgeon for a range of depths of the annulus. That is, the surgeon often pushes the sizer well into the annulus to engage the entire side wall of the sizer, which tends to average the overall resistance to in-and-out movement, and is desired by some surgeons. The central location of the handle connection also balances moments imposed on the sizer as transmitted to the handle. If the sizer is not quite the right size, it is withdrawn and detached from the handle, being replaced by a different sizer. In the insertion or withdrawal steps, the sizer may be accidentally pried off the handle because of the snap fit, though the same attribute of ease of detachment is viewed as a plus to enable rapid switching of different sizers. Additionally, with the trend toward smaller and smaller access channels, the size of devices such as sizers and valves is becoming a limiting factor.
Accordingly, in view of the foregoing, it is an object of the present invention to provide annulus sizers which eliminate many of the drawbacks associated with conventional sizers.
It is an additional object of the present invention to provide annulus sizers which enable a surgeon to clearly view a surgical field.
It is yet another object of the present invention to provide annulus sizers which facilitate annuloplasty procedures through rapid yet secure attachment to handles.
It is still another object of the present invention to provide methodology which enables surgeons to measure the size of valve annuluses in a minimally invasive manner.